Non-tumorigenic mutants of Agrobacterium tumefaciens are being isolated following treatment with chemical mutagens. These mutants will be characterized with respect to the location of their genetic lesions by genetic transfer experiments. Mutations affecting Ti plasmid DNA will be characterized and mapped by complementation analysis using wild-type and mutant Ti plasmid fragments cloned in suitable vectors. Mutations affecting chromosomal genes will be mapped using the R plasmic R68.45 as a sex factor. Derivatives of this R plasmid showing enhanced chromosomal mobilizing activity will be constructed by isolating R's containing portions of the A. tumefaciens chromosome. Such R's will be generated by recombinant DNA technology and used to map the A. tumefaciens chromosome by interrupted mating techniques.